Maps rendering with spaces

When i display a map in a div called venuemap, the map is displayed with gaps.

Example:

http://www.diigo.com/item/image/1w8bo/ck4u

This is the code i use for displaying the map

        /* Open map */
            map = new OpenLayers.Map("venuemap");
            map.addLayer(new OpenLayers.Layer.OSM());

            var lonLat = new OpenLayers.LonLat( venue.location.lng ,venue.location.lat )
                  .transform(
                    new OpenLayers.Projection("EPSG:4326"), // transform from WGS 1984
                    map.getProjectionObject() // to Spherical Mercator Projection
                  );

            var zoom=16;

            var markers = new OpenLayers.Layer.Markers( "Markers" );
            map.addLayer(markers);

            markers.addMarker(new OpenLayers.Marker(lonLat));

            map.setCenter (lonLat, zoom);
            /* end open map */

What is wrong with my code? Kind regards brantje